Microwave alarm

Abstract

A portable microwave power detector is provided which will generate an alarm signal when placed within a microwave field having a power density above a predetermined limit. The detector comprises a rigid body member, a microwave receiving antenna fixed to or within the body member and, between elements of the antenna itself, a passive non-linear audio and/or visual alarm indicator fixed to or within the body member and connected to the antenna for energization by the microwave power received thereby.

The claims defining the invention are as follows: 
     
       1. A microwave alarm device comprising: (a) a rigid body member,   (b) a microwave receiving antenna secured to said body member to prevent relative movement between the body member and said antenna, and between elements of the antenna itself, and   (c) a non-linear alarm indicator secured to the body member and connected to the antenna for energization by microwave power received thereby, said non-linear alarm indicator comprising a hot carrier diode connected across the antenna, a trigger circuit connected across the hot carrier diode and comprising a silicon controlled rectifier and a potential divider circuit connected to the control electrode of the rectifier and across the hot carrier diode, and a passive indicator device connected to said trigger circuit for activation thereby to produce a distinct alarm signal at a predetermined signal level delivered by the diode and antenna combination.   
     
     
       2. A microwave alarm device according to claim 1, wherein the potential divider circuit comprises a zener diode connected in series with a resistor across the hot carrier diode, and wherein the junction of the zener diode and resistor is connected to the control electrode of the silicon controlled rectifier. 
     
     
       3. A microwave alarm device according to claim 1, wherein a second passive indicator device in series with a resistor is connected across the hot carrier diode to provide an indication of the functioning of the hot-carrier diode and antenna combination at microwave radiation intensities below that at which the alarm indicator is activated. 
     
     
       4. A microwave alarm device according to claim 2, wherein a second passive indicator device in series with a resistor is connected across the hot carrier diode to provide an indication of the functioning of the hot-carrier diode and antenna combination at microwave radiation intensities below that at which the alarm indicator is activated. 
     
     
       5. A microwave alarm device comprising: (a) a rigid body member,   (b) a microwave receiving antenna secured to said body member to prevent relative movement between the body member and said antenna, and between elements of the antenna itself, and   (c) a non-linear alarm indicator secured to the body member and connected to the antenna for energization by microwave power received thereby, said non-linear alarm indicator comprising a hot carrier diode connected across the antenna, a trigger circuit connected across the hot carrier diode, and a passive indicator device connected to said trigger circuit for activation thereby to produce a distinct alarm signal at a predetermined signal level delivered by the diode and antenna combination.   
     
     
       6. A microwave alarm device comprising: a rigid body member, a microwave receiving antenna secured to said body member to prevent relative movement between the body member and said antenna, and between elements of the antenna itself, and a passive, non-linear alarm indicator secured to the body member and connected to the antenna for energization by microwave power received thereby; said non-linear alarm indicator comprising a miniature filament lamp connected directly to the antenna, wherein the filament wire of the lamp is wound in coils such that the ratio of the coil length to the length of the wire comprising the coils is within the range 0.1 to 0.4, the lamp having a nominal DC rating of 12 volts or less and 100 to 500 m.watt, wherein, upon subjecting the device to a microwave field of increasing intensity, the alarm indicator is activated by the microwave energy supplied from the antenna to produce a distinct visual alarm signal when the energy of the microwave field exceeds a predetermined level.